yeah It was used for my Nex 5n. Just experimenting on my A7 It is turning the 28mm approximately into a 18mm lens but since the sides are kind of distorted I think it makes for a good way to do square image or even a panoramic photo.

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I got rid of my next 5n when I got the a7 that's why I still have this. And yes MF lenses are the best choice for this on a nex. I am hoping to find a lens in my collection that will skirt the vignette in 16:9 mode

One of my favorites on the K5 is also a gem on the A7 - the Pentax-A 100mm f2.8 macro. Perhaps the autofocus successors are as good optically, but ergonomically the A is much better. Focus is so nice and smooth, damped yet operable with one finger, huge focus ring. A pleasure. And the 1:1 ability is really important. Some samples;